Alignments
An alignment is the horizontal path of a road, pipe or channel: straights joined by curves, measured by chainage. Learn to lay one out and label it.
In this lesson you will
- Create an alignment with the layout tools
- Understand tangents, curves and spirals
- Apply design criteria
- Label and edit stations/chainage
What an alignment is
A horizontal alignment is made of tangents (straights), curves (arcs) and optionally spirals (transition curves). Position along it is measured as station or chainage — e.g. 0+250 is 250 m from the start. Profiles, corridors, sections and setting-out all reference the alignment.
Creating one
- 1Home › Alignment › Alignment Creation Tools.
- 2Name it (Road A CL), choose type (Centerline), style and label set, and set the starting station.
- 3Choose Tangent–Tangent (with curves) and set the default curve radius.
- 4Click the points of intersection (PIs) along the route; curves are added automatically at each PI.
- 5Or create from an existing polyline and then refine.
Design criteria
Tick Use criteria-based design and choose a design speed and criteria file (e.g. AASHTO or a regional standard). Civil 3D flags curves with a radius below the minimum for the speed. Use the standard your road authority requires — design criteria are not universal.
Editing and labels
Drag PI grips to reshape; use the Alignment Layout Parameters table to type exact radii and lengths. Labels show major and minor chainage ticks and geometry points (TS, SC, PC, PT). The Alignment Grid View lists every element.
Quick reference
| Command / tool | How to start it | What it does |
|---|---|---|
| Alignment Creation Tools | Home › Alignment | Lays out alignments |
| Create from Objects | Home › Alignment | Alignment from a polyline |
| Geometry Editor | Select alignment | Edits sub-entities |
| Station labels | Label set | Chainage ticks and points |
Common mistakes
Curves flagged as violating criteria.
Increase radii or reduce design speed per the standard.
Chainage starts at the wrong end.
Reverse the alignment direction or set the start station.
Exercise
A road centreline
- Draw a 400 m alignment across your surface with two PIs and 150 m curves.
- Turn on design criteria for 60 km/h and review warnings.
- Label chainage every 20 m (minor) and 100 m (major).
- Edit a curve radius in the parameters table.
You should end up with: A labelled, criteria-checked alignment.
Checklist
0 of 4 checked · saved on this device
Lesson quiz
Chainage 0+250 means 250 m along the alignment.
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